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Linux/mm/mremap.c

  1 /*
  2  *      mm/mremap.c
  3  *
  4  *      (C) Copyright 1996 Linus Torvalds
  5  *
  6  *      Address space accounting code   <alan@lxorguk.ukuu.org.uk>
  7  *      (C) Copyright 2002 Red Hat Inc, All Rights Reserved
  8  */
  9 
 10 #include <linux/mm.h>
 11 #include <linux/hugetlb.h>
 12 #include <linux/shm.h>
 13 #include <linux/ksm.h>
 14 #include <linux/mman.h>
 15 #include <linux/swap.h>
 16 #include <linux/capability.h>
 17 #include <linux/fs.h>
 18 #include <linux/swapops.h>
 19 #include <linux/highmem.h>
 20 #include <linux/security.h>
 21 #include <linux/syscalls.h>
 22 #include <linux/mmu_notifier.h>
 23 #include <linux/sched/sysctl.h>
 24 #include <linux/uaccess.h>
 25 #include <linux/mm-arch-hooks.h>
 26 
 27 #include <asm/cacheflush.h>
 28 #include <asm/tlbflush.h>
 29 
 30 #include "internal.h"
 31 
 32 static pmd_t *get_old_pmd(struct mm_struct *mm, unsigned long addr)
 33 {
 34         pgd_t *pgd;
 35         pud_t *pud;
 36         pmd_t *pmd;
 37 
 38         pgd = pgd_offset(mm, addr);
 39         if (pgd_none_or_clear_bad(pgd))
 40                 return NULL;
 41 
 42         pud = pud_offset(pgd, addr);
 43         if (pud_none_or_clear_bad(pud))
 44                 return NULL;
 45 
 46         pmd = pmd_offset(pud, addr);
 47         if (pmd_none(*pmd))
 48                 return NULL;
 49 
 50         return pmd;
 51 }
 52 
 53 static pmd_t *alloc_new_pmd(struct mm_struct *mm, struct vm_area_struct *vma,
 54                             unsigned long addr)
 55 {
 56         pgd_t *pgd;
 57         pud_t *pud;
 58         pmd_t *pmd;
 59 
 60         pgd = pgd_offset(mm, addr);
 61         pud = pud_alloc(mm, pgd, addr);
 62         if (!pud)
 63                 return NULL;
 64 
 65         pmd = pmd_alloc(mm, pud, addr);
 66         if (!pmd)
 67                 return NULL;
 68 
 69         VM_BUG_ON(pmd_trans_huge(*pmd));
 70 
 71         return pmd;
 72 }
 73 
 74 static pte_t move_soft_dirty_pte(pte_t pte)
 75 {
 76         /*
 77          * Set soft dirty bit so we can notice
 78          * in userspace the ptes were moved.
 79          */
 80 #ifdef CONFIG_MEM_SOFT_DIRTY
 81         if (pte_present(pte))
 82                 pte = pte_mksoft_dirty(pte);
 83         else if (is_swap_pte(pte))
 84                 pte = pte_swp_mksoft_dirty(pte);
 85 #endif
 86         return pte;
 87 }
 88 
 89 static void move_ptes(struct vm_area_struct *vma, pmd_t *old_pmd,
 90                 unsigned long old_addr, unsigned long old_end,
 91                 struct vm_area_struct *new_vma, pmd_t *new_pmd,
 92                 unsigned long new_addr, bool need_rmap_locks)
 93 {
 94         struct address_space *mapping = NULL;
 95         struct anon_vma *anon_vma = NULL;
 96         struct mm_struct *mm = vma->vm_mm;
 97         pte_t *old_pte, *new_pte, pte;
 98         spinlock_t *old_ptl, *new_ptl;
 99 
100         /*
101          * When need_rmap_locks is true, we take the i_mmap_rwsem and anon_vma
102          * locks to ensure that rmap will always observe either the old or the
103          * new ptes. This is the easiest way to avoid races with
104          * truncate_pagecache(), page migration, etc...
105          *
106          * When need_rmap_locks is false, we use other ways to avoid
107          * such races:
108          *
109          * - During exec() shift_arg_pages(), we use a specially tagged vma
110          *   which rmap call sites look for using is_vma_temporary_stack().
111          *
112          * - During mremap(), new_vma is often known to be placed after vma
113          *   in rmap traversal order. This ensures rmap will always observe
114          *   either the old pte, or the new pte, or both (the page table locks
115          *   serialize access to individual ptes, but only rmap traversal
116          *   order guarantees that we won't miss both the old and new ptes).
117          */
118         if (need_rmap_locks) {
119                 if (vma->vm_file) {
120                         mapping = vma->vm_file->f_mapping;
121                         i_mmap_lock_write(mapping);
122                 }
123                 if (vma->anon_vma) {
124                         anon_vma = vma->anon_vma;
125                         anon_vma_lock_write(anon_vma);
126                 }
127         }
128 
129         /*
130          * We don't have to worry about the ordering of src and dst
131          * pte locks because exclusive mmap_sem prevents deadlock.
132          */
133         old_pte = pte_offset_map_lock(mm, old_pmd, old_addr, &old_ptl);
134         new_pte = pte_offset_map(new_pmd, new_addr);
135         new_ptl = pte_lockptr(mm, new_pmd);
136         if (new_ptl != old_ptl)
137                 spin_lock_nested(new_ptl, SINGLE_DEPTH_NESTING);
138         arch_enter_lazy_mmu_mode();
139 
140         for (; old_addr < old_end; old_pte++, old_addr += PAGE_SIZE,
141                                    new_pte++, new_addr += PAGE_SIZE) {
142                 if (pte_none(*old_pte))
143                         continue;
144                 pte = ptep_get_and_clear(mm, old_addr, old_pte);
145                 pte = move_pte(pte, new_vma->vm_page_prot, old_addr, new_addr);
146                 pte = move_soft_dirty_pte(pte);
147                 set_pte_at(mm, new_addr, new_pte, pte);
148         }
149 
150         arch_leave_lazy_mmu_mode();
151         if (new_ptl != old_ptl)
152                 spin_unlock(new_ptl);
153         pte_unmap(new_pte - 1);
154         pte_unmap_unlock(old_pte - 1, old_ptl);
155         if (anon_vma)
156                 anon_vma_unlock_write(anon_vma);
157         if (mapping)
158                 i_mmap_unlock_write(mapping);
159 }
160 
161 #define LATENCY_LIMIT   (64 * PAGE_SIZE)
162 
163 unsigned long move_page_tables(struct vm_area_struct *vma,
164                 unsigned long old_addr, struct vm_area_struct *new_vma,
165                 unsigned long new_addr, unsigned long len,
166                 bool need_rmap_locks)
167 {
168         unsigned long extent, next, old_end;
169         pmd_t *old_pmd, *new_pmd;
170         bool need_flush = false;
171         unsigned long mmun_start;       /* For mmu_notifiers */
172         unsigned long mmun_end;         /* For mmu_notifiers */
173 
174         old_end = old_addr + len;
175         flush_cache_range(vma, old_addr, old_end);
176 
177         mmun_start = old_addr;
178         mmun_end   = old_end;
179         mmu_notifier_invalidate_range_start(vma->vm_mm, mmun_start, mmun_end);
180 
181         for (; old_addr < old_end; old_addr += extent, new_addr += extent) {
182                 cond_resched();
183                 next = (old_addr + PMD_SIZE) & PMD_MASK;
184                 /* even if next overflowed, extent below will be ok */
185                 extent = next - old_addr;
186                 if (extent > old_end - old_addr)
187                         extent = old_end - old_addr;
188                 old_pmd = get_old_pmd(vma->vm_mm, old_addr);
189                 if (!old_pmd)
190                         continue;
191                 new_pmd = alloc_new_pmd(vma->vm_mm, vma, new_addr);
192                 if (!new_pmd)
193                         break;
194                 if (pmd_trans_huge(*old_pmd)) {
195                         int err = 0;
196                         if (extent == HPAGE_PMD_SIZE) {
197                                 VM_BUG_ON_VMA(vma->vm_file || !vma->anon_vma,
198                                               vma);
199                                 /* See comment in move_ptes() */
200                                 if (need_rmap_locks)
201                                         anon_vma_lock_write(vma->anon_vma);
202                                 err = move_huge_pmd(vma, new_vma, old_addr,
203                                                     new_addr, old_end,
204                                                     old_pmd, new_pmd);
205                                 if (need_rmap_locks)
206                                         anon_vma_unlock_write(vma->anon_vma);
207                         }
208                         if (err > 0) {
209                                 need_flush = true;
210                                 continue;
211                         } else if (!err) {
212                                 split_huge_page_pmd(vma, old_addr, old_pmd);
213                         }
214                         VM_BUG_ON(pmd_trans_huge(*old_pmd));
215                 }
216                 if (pmd_none(*new_pmd) && __pte_alloc(new_vma->vm_mm, new_vma,
217                                                       new_pmd, new_addr))
218                         break;
219                 next = (new_addr + PMD_SIZE) & PMD_MASK;
220                 if (extent > next - new_addr)
221                         extent = next - new_addr;
222                 if (extent > LATENCY_LIMIT)
223                         extent = LATENCY_LIMIT;
224                 move_ptes(vma, old_pmd, old_addr, old_addr + extent,
225                           new_vma, new_pmd, new_addr, need_rmap_locks);
226                 need_flush = true;
227         }
228         if (likely(need_flush))
229                 flush_tlb_range(vma, old_end-len, old_addr);
230 
231         mmu_notifier_invalidate_range_end(vma->vm_mm, mmun_start, mmun_end);
232 
233         return len + old_addr - old_end;        /* how much done */
234 }
235 
236 static unsigned long move_vma(struct vm_area_struct *vma,
237                 unsigned long old_addr, unsigned long old_len,
238                 unsigned long new_len, unsigned long new_addr, bool *locked)
239 {
240         struct mm_struct *mm = vma->vm_mm;
241         struct vm_area_struct *new_vma;
242         unsigned long vm_flags = vma->vm_flags;
243         unsigned long new_pgoff;
244         unsigned long moved_len;
245         unsigned long excess = 0;
246         unsigned long hiwater_vm;
247         int split = 0;
248         int err;
249         bool need_rmap_locks;
250 
251         /*
252          * We'd prefer to avoid failure later on in do_munmap:
253          * which may split one vma into three before unmapping.
254          */
255         if (mm->map_count >= sysctl_max_map_count - 3)
256                 return -ENOMEM;
257 
258         /*
259          * Advise KSM to break any KSM pages in the area to be moved:
260          * it would be confusing if they were to turn up at the new
261          * location, where they happen to coincide with different KSM
262          * pages recently unmapped.  But leave vma->vm_flags as it was,
263          * so KSM can come around to merge on vma and new_vma afterwards.
264          */
265         err = ksm_madvise(vma, old_addr, old_addr + old_len,
266                                                 MADV_UNMERGEABLE, &vm_flags);
267         if (err)
268                 return err;
269 
270         new_pgoff = vma->vm_pgoff + ((old_addr - vma->vm_start) >> PAGE_SHIFT);
271         new_vma = copy_vma(&vma, new_addr, new_len, new_pgoff,
272                            &need_rmap_locks);
273         if (!new_vma)
274                 return -ENOMEM;
275 
276         moved_len = move_page_tables(vma, old_addr, new_vma, new_addr, old_len,
277                                      need_rmap_locks);
278         if (moved_len < old_len) {
279                 /*
280                  * On error, move entries back from new area to old,
281                  * which will succeed since page tables still there,
282                  * and then proceed to unmap new area instead of old.
283                  */
284                 move_page_tables(new_vma, new_addr, vma, old_addr, moved_len,
285                                  true);
286                 vma = new_vma;
287                 old_len = new_len;
288                 old_addr = new_addr;
289                 new_addr = -ENOMEM;
290         } else {
291                 if (vma->vm_file && vma->vm_file->f_op->mremap) {
292                         err = vma->vm_file->f_op->mremap(vma->vm_file, new_vma);
293                         if (err < 0) {
294                                 move_page_tables(new_vma, new_addr, vma,
295                                                  old_addr, moved_len, true);
296                                 return err;
297                         }
298                 }
299                 arch_remap(mm, old_addr, old_addr + old_len,
300                            new_addr, new_addr + new_len);
301         }
302 
303         /* Conceal VM_ACCOUNT so old reservation is not undone */
304         if (vm_flags & VM_ACCOUNT) {
305                 vma->vm_flags &= ~VM_ACCOUNT;
306                 excess = vma->vm_end - vma->vm_start - old_len;
307                 if (old_addr > vma->vm_start &&
308                     old_addr + old_len < vma->vm_end)
309                         split = 1;
310         }
311 
312         /*
313          * If we failed to move page tables we still do total_vm increment
314          * since do_munmap() will decrement it by old_len == new_len.
315          *
316          * Since total_vm is about to be raised artificially high for a
317          * moment, we need to restore high watermark afterwards: if stats
318          * are taken meanwhile, total_vm and hiwater_vm appear too high.
319          * If this were a serious issue, we'd add a flag to do_munmap().
320          */
321         hiwater_vm = mm->hiwater_vm;
322         vm_stat_account(mm, vma->vm_flags, vma->vm_file, new_len>>PAGE_SHIFT);
323 
324         if (do_munmap(mm, old_addr, old_len) < 0) {
325                 /* OOM: unable to split vma, just get accounts right */
326                 vm_unacct_memory(excess >> PAGE_SHIFT);
327                 excess = 0;
328         }
329         mm->hiwater_vm = hiwater_vm;
330 
331         /* Restore VM_ACCOUNT if one or two pieces of vma left */
332         if (excess) {
333                 vma->vm_flags |= VM_ACCOUNT;
334                 if (split)
335                         vma->vm_next->vm_flags |= VM_ACCOUNT;
336         }
337 
338         if (vm_flags & VM_LOCKED) {
339                 mm->locked_vm += new_len >> PAGE_SHIFT;
340                 *locked = true;
341         }
342 
343         return new_addr;
344 }
345 
346 static struct vm_area_struct *vma_to_resize(unsigned long addr,
347         unsigned long old_len, unsigned long new_len, unsigned long *p)
348 {
349         struct mm_struct *mm = current->mm;
350         struct vm_area_struct *vma = find_vma(mm, addr);
351 
352         if (!vma || vma->vm_start > addr)
353                 return ERR_PTR(-EFAULT);
354 
355         if (is_vm_hugetlb_page(vma))
356                 return ERR_PTR(-EINVAL);
357 
358         /* We can't remap across vm area boundaries */
359         if (old_len > vma->vm_end - addr)
360                 return ERR_PTR(-EFAULT);
361 
362         /* Need to be careful about a growing mapping */
363         if (new_len > old_len) {
364                 unsigned long pgoff;
365 
366                 if (vma->vm_flags & (VM_DONTEXPAND | VM_PFNMAP))
367                         return ERR_PTR(-EFAULT);
368                 pgoff = (addr - vma->vm_start) >> PAGE_SHIFT;
369                 pgoff += vma->vm_pgoff;
370                 if (pgoff + (new_len >> PAGE_SHIFT) < pgoff)
371                         return ERR_PTR(-EINVAL);
372         }
373 
374         if (vma->vm_flags & VM_LOCKED) {
375                 unsigned long locked, lock_limit;
376                 locked = mm->locked_vm << PAGE_SHIFT;
377                 lock_limit = rlimit(RLIMIT_MEMLOCK);
378                 locked += new_len - old_len;
379                 if (locked > lock_limit && !capable(CAP_IPC_LOCK))
380                         return ERR_PTR(-EAGAIN);
381         }
382 
383         if (!may_expand_vm(mm, (new_len - old_len) >> PAGE_SHIFT))
384                 return ERR_PTR(-ENOMEM);
385 
386         if (vma->vm_flags & VM_ACCOUNT) {
387                 unsigned long charged = (new_len - old_len) >> PAGE_SHIFT;
388                 if (security_vm_enough_memory_mm(mm, charged))
389                         return ERR_PTR(-ENOMEM);
390                 *p = charged;
391         }
392 
393         return vma;
394 }
395 
396 static unsigned long mremap_to(unsigned long addr, unsigned long old_len,
397                 unsigned long new_addr, unsigned long new_len, bool *locked)
398 {
399         struct mm_struct *mm = current->mm;
400         struct vm_area_struct *vma;
401         unsigned long ret = -EINVAL;
402         unsigned long charged = 0;
403         unsigned long map_flags;
404 
405         if (new_addr & ~PAGE_MASK)
406                 goto out;
407 
408         if (new_len > TASK_SIZE || new_addr > TASK_SIZE - new_len)
409                 goto out;
410 
411         /* Check if the location we're moving into overlaps the
412          * old location at all, and fail if it does.
413          */
414         if ((new_addr <= addr) && (new_addr+new_len) > addr)
415                 goto out;
416 
417         if ((addr <= new_addr) && (addr+old_len) > new_addr)
418                 goto out;
419 
420         ret = do_munmap(mm, new_addr, new_len);
421         if (ret)
422                 goto out;
423 
424         if (old_len >= new_len) {
425                 ret = do_munmap(mm, addr+new_len, old_len - new_len);
426                 if (ret && old_len != new_len)
427                         goto out;
428                 old_len = new_len;
429         }
430 
431         vma = vma_to_resize(addr, old_len, new_len, &charged);
432         if (IS_ERR(vma)) {
433                 ret = PTR_ERR(vma);
434                 goto out;
435         }
436 
437         map_flags = MAP_FIXED;
438         if (vma->vm_flags & VM_MAYSHARE)
439                 map_flags |= MAP_SHARED;
440 
441         ret = get_unmapped_area(vma->vm_file, new_addr, new_len, vma->vm_pgoff +
442                                 ((addr - vma->vm_start) >> PAGE_SHIFT),
443                                 map_flags);
444         if (ret & ~PAGE_MASK)
445                 goto out1;
446 
447         ret = move_vma(vma, addr, old_len, new_len, new_addr, locked);
448         if (!(ret & ~PAGE_MASK))
449                 goto out;
450 out1:
451         vm_unacct_memory(charged);
452 
453 out:
454         return ret;
455 }
456 
457 static int vma_expandable(struct vm_area_struct *vma, unsigned long delta)
458 {
459         unsigned long end = vma->vm_end + delta;
460         if (end < vma->vm_end) /* overflow */
461                 return 0;
462         if (vma->vm_next && vma->vm_next->vm_start < end) /* intersection */
463                 return 0;
464         if (get_unmapped_area(NULL, vma->vm_start, end - vma->vm_start,
465                               0, MAP_FIXED) & ~PAGE_MASK)
466                 return 0;
467         return 1;
468 }
469 
470 /*
471  * Expand (or shrink) an existing mapping, potentially moving it at the
472  * same time (controlled by the MREMAP_MAYMOVE flag and available VM space)
473  *
474  * MREMAP_FIXED option added 5-Dec-1999 by Benjamin LaHaise
475  * This option implies MREMAP_MAYMOVE.
476  */
477 SYSCALL_DEFINE5(mremap, unsigned long, addr, unsigned long, old_len,
478                 unsigned long, new_len, unsigned long, flags,
479                 unsigned long, new_addr)
480 {
481         struct mm_struct *mm = current->mm;
482         struct vm_area_struct *vma;
483         unsigned long ret = -EINVAL;
484         unsigned long charged = 0;
485         bool locked = false;
486 
487         if (flags & ~(MREMAP_FIXED | MREMAP_MAYMOVE))
488                 return ret;
489 
490         if (flags & MREMAP_FIXED && !(flags & MREMAP_MAYMOVE))
491                 return ret;
492 
493         if (addr & ~PAGE_MASK)
494                 return ret;
495 
496         old_len = PAGE_ALIGN(old_len);
497         new_len = PAGE_ALIGN(new_len);
498 
499         /*
500          * We allow a zero old-len as a special case
501          * for DOS-emu "duplicate shm area" thing. But
502          * a zero new-len is nonsensical.
503          */
504         if (!new_len)
505                 return ret;
506 
507         down_write(&current->mm->mmap_sem);
508 
509         if (flags & MREMAP_FIXED) {
510                 ret = mremap_to(addr, old_len, new_addr, new_len,
511                                 &locked);
512                 goto out;
513         }
514 
515         /*
516          * Always allow a shrinking remap: that just unmaps
517          * the unnecessary pages..
518          * do_munmap does all the needed commit accounting
519          */
520         if (old_len >= new_len) {
521                 ret = do_munmap(mm, addr+new_len, old_len - new_len);
522                 if (ret && old_len != new_len)
523                         goto out;
524                 ret = addr;
525                 goto out;
526         }
527 
528         /*
529          * Ok, we need to grow..
530          */
531         vma = vma_to_resize(addr, old_len, new_len, &charged);
532         if (IS_ERR(vma)) {
533                 ret = PTR_ERR(vma);
534                 goto out;
535         }
536 
537         /* old_len exactly to the end of the area..
538          */
539         if (old_len == vma->vm_end - addr) {
540                 /* can we just expand the current mapping? */
541                 if (vma_expandable(vma, new_len - old_len)) {
542                         int pages = (new_len - old_len) >> PAGE_SHIFT;
543 
544                         if (vma_adjust(vma, vma->vm_start, addr + new_len,
545                                        vma->vm_pgoff, NULL)) {
546                                 ret = -ENOMEM;
547                                 goto out;
548                         }
549 
550                         vm_stat_account(mm, vma->vm_flags, vma->vm_file, pages);
551                         if (vma->vm_flags & VM_LOCKED) {
552                                 mm->locked_vm += pages;
553                                 locked = true;
554                                 new_addr = addr;
555                         }
556                         ret = addr;
557                         goto out;
558                 }
559         }
560 
561         /*
562          * We weren't able to just expand or shrink the area,
563          * we need to create a new one and move it..
564          */
565         ret = -ENOMEM;
566         if (flags & MREMAP_MAYMOVE) {
567                 unsigned long map_flags = 0;
568                 if (vma->vm_flags & VM_MAYSHARE)
569                         map_flags |= MAP_SHARED;
570 
571                 new_addr = get_unmapped_area(vma->vm_file, 0, new_len,
572                                         vma->vm_pgoff +
573                                         ((addr - vma->vm_start) >> PAGE_SHIFT),
574                                         map_flags);
575                 if (new_addr & ~PAGE_MASK) {
576                         ret = new_addr;
577                         goto out;
578                 }
579 
580                 ret = move_vma(vma, addr, old_len, new_len, new_addr, &locked);
581         }
582 out:
583         if (ret & ~PAGE_MASK)
584                 vm_unacct_memory(charged);
585         up_write(&current->mm->mmap_sem);
586         if (locked && new_len > old_len)
587                 mm_populate(new_addr + old_len, new_len - old_len);
588         return ret;
589 }
590 

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